Solving ODE in MATLAB with pre-defined steps

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Johannsen
Johannsen 2022-10-22
编辑： Johannsen 2022-10-23
Hello,
I would like to solve an ordinary differential equations (ODE) with a specfic step using the command ode45. The equation has a range between 0 and 2.75 and the intial condition is 1
F=@(R,t)((R/t_a)*((CFS(1,i))/(0.25*taw_0)-R))
[t,R]=ode45(F, [0 2.75], 1)
In this case, Matlab provides a set of values (41 values). For example, t is a set of values range between 0 and 2.75.
How can I specify that I do not want random values of t in the ODE? Here, I want t to range between 0 and 2.75 but I want a step size of 0.25
Thanks,

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回答（2 个）

Star Strider
Star Strider 2022-10-22
Ran in:
‘How can I specify that I do not want random values of t in the ODE? Here, I want t to range between 0 and 2.75 but I want a step size of 0.25’
Create ‘tspan’ as a vector of more than two elements.
Specifically —
tspan = 0 : 0.25 : 2.75
tspan = 1×12
0 0.2500 0.5000 0.7500 1.0000 1.2500 1.5000 1.7500 2.0000 2.2500 2.5000 2.7500
Then use that for the ‘tspan’ argument.
The ordinary differential equations integrators will work adaptively as usual, however they will only report results at those times.
.
Torsten
Torsten 2022-10-22
You can't choose the step size of ODE45 because the solver adapts the step size internally. You can only choose the output times by setting the variable "tspan".

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